This invention relates to an optical gate signal generating apparatus and relates to a thyristor converter apparatus with an optical gate signal generating apparatus which is fired in accordance with the optical gate signal.
Conventionally an optical gate signal generating apparatus includes a control circuit for generating an electrical gate signal, and a plurality of light emitting elements each generating an optical gate signal upon receipt of the electrical gate signal for firing each of a plurality of thyristors in a thyristor converter apparatus. Such firing method has been developed from the result of the light transmission technique which is rapidly advancing in recent years. Due to improvement on the property of a light-triggered thyristor which is directly operated by an optical signal, the technique has come to be widely accepted which comprises the steps of transmitting an optical signal generated from a light emitting element through a light guide and carrying out the firing of the light-triggered thyristor by the direct application of an optical signal.
Description is now given with reference to FIG. 1 of a conventional optical gate signal generating apparatus 10. The optical gate signal generating apparatus 10 is so arranged as to control a thyristor converter apparatus 12 through a light guide. The thyristor converter apparatus is generally constituted by a plurality of light-triggered thyristors arranged in a multiphase connection. An optical gate signal generating apparatus is provided for each phase. Since all the phases have the same construction, FIG. 1 indicates a circuit diagram of only one phase or arm. The optical gate signal generating apparatus 10 comprises a plurality of light emitting elements A11, A12 . . . Amn such as light-emitting diodes or laser diodes. The thyristor converter apparatus 12 comprises light-triggered thyristors B11, B12 . . . Bmn corresponding to the above-mentioned light emitting elements A11, A12 . . . Amn. Light emitting elements and light-triggered thyristors having the same suffix are connected by light guides C11, C12 . . . Cmn bearing the same suffix. When every constituent member need not be distinguished with respect to the groups of the light emitting elements, light-triggered thyristors and light guides, then the light emitting elements, the light-triggered thyristors, and the light guides are collectively represented by A, B and C, respectively. For briefness, FIG. 1 shows only one light guide C11. All the light-triggered thyristors B and a single anode reactor 16 are connected in series between power supply terminals E1 and E2. Each light-triggered thyristor B is connected in parallel to a series circuit including a resistor 20 and a capacitor 22. A resistor 24 is further connected in parallel with the series circuit. The anode reactor 16 is used to control the rate of increase of the current, with respect to time, flowing through the firing light-triggered thyristors B. The resistors 20, 24 and capacitor 22 jointly constitute a voltage-dividing circuit. Description is omitted of the operation of the circuit which is already known.
The optical signal generating apparatus 10 is provided with a control circuit 36, which comprises a gate signal generating circuit or gate signal generator 32, an amplifier 34 and a transistor 30. The m.times.n light emitting elements, in which m and n are positive integer numbers, are connected in a network including m parallel circuits each comprising n light emitting elements connected in series. Each series circuit constitutes a parallel circuit with a diodes 26. Each of the parallel circuits is connected at one end to a positive power supply terminal F1 through a resistor 28, and at the other end to a negative power supply terminal F2 through the transistor 30. All the light emitting elements A are connected to the power supply terminals F1, F2 in the forward direction and all the diodes 26 are connected with respect to the supply terminals F1, F2 in the reverse direction.
The gate signal generating circuit 32 included in the control circuit 36 generates an electrical gate signal defining a timing in which a light emitting element is to be operated. The output signal is amplified by the amplifier 34, and then delivered to the transistor 30. The transistor 30 switches on or switches off the power supply circuits F1, F2 in accordance with the contents of the signal received. As a result, when voltage is applied on the aforesaid m parallel arranged circuits and current flows through each of the m parallel circuits, then all the light emitting elements A are simultaneously fired in the aforementioned timing. Each optical gate signal generated from the light-emitting element A is conducted through the light guide C to the corresponding light-triggered thyristor B, which in turn is fired in the aforementioned timing. Therefore, the voltage (takes a value about one-m.times.nth of the source voltage between power terminals E1 and E2) applied on each of the thyristors B at this time changes substantially to zero.
The conventional optical gate signal generating apparatus 10 of FIG. 1 is indeed useful, but is still accompanied with drawbacks. These drawbacks are the very problems for whose resolution this invention is primarily intended. Namely, the prior art optical gate signal generating apparatus has the difficulties as follows. When an open fault arises in any of the light emitting elements A constituting one of the series circuits arranged in parallel in a number of m, the current flowing through the series circuit including the defective light emitting element A is cut off. Among m.times.n light-triggered thyristors connected in series in the thyristor converter apparatus 12, n light-triggered thyristors B connected by the light guides C to the series circuit including the defective light-emitting element A are not fired. Consequently the voltage applied up to this time on the series circuit consisting of m.times.n light-triggered thyristors is now applied to the n light-triggered thyristors corresponding to the aforesaid defective series circuit of light emitting elements A. Therefore n light-triggered thyristors are damaged due to application of excessively high voltage, thereby disenabling the thyristor converter apparatus 12.
To resolve the aforementioned drawbacks and increase the reliablility of the thyristor converter apparatus, it has been contemplated to provide a multi-type optical gate signal generating apparatus shown in FIG. 2. The multi-type optical gate signal generating apparatus constructed by providing two optical gate signal generating apparatuses, for example, 10a, 10b and connecting corresponding light emitting elements A1, A2 of the optical gate signal generating apparatuses 10a, 10b to one of the light-triggered thyristors B through a light guide Da. This multi-type optical gate signal generating apparatus indeed has the advantage that even when one of said paired optical gate signal generating apparatuses fails, the operation of the thyristor converter apparatus 12 can be continued. But the multi-type optical gate signal generating apparatus still has the drawbacks as follows. The provision of the two, for example, control circuits 36a, 36b leads to larger power consumption. All the light emitting elements A1, A2 included in the multi-type optical gate signal generating apparatus are always rendered conductive and consequently deteriorated substantially at the same rate. As a plurality of optical gate signal generating apparatuses are provided in the multi-type apparatus, the construction as well as the electric circuit thereof becomes dual and complicated. And the application of numerous parts undesirably raises the failure rate with which failures arise, thereby reducing the reliability of the multiple-type optical gate signal generating apparatus as a whole.